1. Field of the Invention
The present invention relates to an exercise apparatus as normally used to perform physical exercise based on walking or running, as well as to measure the physical characteristics of athletes or people undergoing clinical tests under specified and controlled fatigue conditions.
Such machines are generally known in the art under the name of running/walking machines, or treadmills.
In particular, the present invention relates to the control and protection arrangements that are provided against possible failures and improper operation of the machine that might cause the user to suffer injuries.
2. Description of Related Art
Physical exercise machines of the above described kind are known in which a horizontally sliding belt driven by a motor determines the rate or speed of walking or running which the user desires to maintain in order to stay on the belt.
Such machines comprise arrangements to control and regulate the speed of the belt in accordance with appropriate commands that are entered and stored in a computer control system. In such control arrangements, the feedback signal that represents the actual speed of the belt is generated by an appropriate sensor, or encoder, which may, for instance, be constituted by an optical sensor or a tachometer.
The speed control system of the motor compares the command signals with the speed feedback signal and the detected deviation is used to correct and adjust the voltage applied to the input terminals of the motor accordingly.
If, for any reason, the feedback signal is lost, the automatic speed control system, if protective precautions are lacking, will act as if the belt has stopped and, therefore, a speed-up demand will be generated and transmitted to the motor, so that the speed will rapidly reach its highest possible value.
As a result, a sudden and spontaneous increase in the motor and, hence, belt speed in these machines would most probably find the user unprepared and throw the same user backward with a powerful force, since the belt is moving toward the rear with respect to the position of the user.
In view of eliminating such a possible cause of accident, it is known in the art to provide safety devices and design arrangements in the central control unit (CPU) so as to avoid incurring such hazardous situations as described. Such safety arrangements include the provision of so-called "watchdog" circuits, i.e. circuits that are adapted to prevent such accidents from occurring and to stop the operation of the machine also in the case of an improper operation or a failure of said safety circuits. However, all such prior art solutions have a number of functional and safety drawbacks that will be shortly described below:
A) If the major causes that may give rise to a runaway speed condition of the belt-driving motor are examined, they will be found to be determined by any of the following conditions:
a short-circuit condition of the power switch; PA1 a demand for abnormal input to the motor control circuits, particularly a permanent demand for maximum speed; and PA1 an interruption of the speed feedback signal sent by the speed sensor, usually an encoder.
While a malfunction condition concerning the encoder may well be recognized from the detection based on the speed error (although it should be noticed that a runaway speed condition of the motor may only occur when the CPU closes the speed loop), the recognition of the other two types of malfunction is not effective when done with this type of method.
As a matter of fact, since the prior art method is based on the reading of the number of pulses of the encoder (on the basis of a unit of time) or on a measurement of the time between consecutive pulses, the prior art solution is linked to the mechanical time constant of the system.
If, for instance, the power switch enters a short-circuit condition, it becomes necessary to wait for the motor to increase its speed before this increase in speed can be read through the encoder and, as a result, an error-proof and fail-safe switching off can occur. This may require up to several hundred milliseconds in systems in which the motor response is a quick one and speed jerks are dangerous for the safety of the user.
It should be noticed that the minimum actual time of detection of the short-circuit condition in the power switch is linked to the electric time constant.
B) Prior art solutions are not provided with any means adapted to detect a malfunction condition with the motor at a standstill. This gives rise to a real hazardous condition in that, if the machine is switched on and the motor power-supply switch is in a failure state, the walking/running surface starts moving abruptly under the highest possible acceleration, with resulting possible risks of accident and injury to the user.